LCD units are often employed as the display devices in numerous products. A typical LCD unit comprises an LCD panel that includes a plurality of polarized crystals which, upon the application of a predetermined electric field from an external source, form a desired image that displays specific information. As such, information can be quickly displayed and modified with little energy and no moving parts.
LCD panels are merely light receiving devices, and as such do not themselves emit light. As a result, in many applications an LCD unit may also employ a backlight unit to provide the LCD panel with sufficient light that the information displayed can be seen easily. The backlight unit includes a lamp assembly and a series of overlying sheets that receive and modify the character of the light. Generally, the lamp assembly is formed as an integrated unit that can be easily replaced when its performance deteriorates. The overlying sheets typically include, in order, a protecting sheet, a prism sheet, a diffusing sheet, a light guide plate and a reflecting sheet. Both the lamp assembly and the overlying sheets are mounted within a mold frame, wherein the lamp assembly is inserted into one or both ends of the light guide plate. In order to prevent the light guide plate and the sheets from moving toward the lamp assembly, guide members are formed on the mold frame. Right-angled guide grooves are formed on the corners of the light guide plate and the sheets opposed to the guide member. The guide members are fit in the right-angled guide grooves.
After assembling the lamp assembly, the light guide plate, and the sheets under the backside of the mold frame, a back cover under the mold frame encloses the above components. At this time, the reflecting sheet and the back cover are spaced apart from each other. The guide members and the back cover are also spaced apart from each other to provide desired design margins.
A problem is presented in that, when the LCD is subjected to an impact test and a vibration test, the reflecting sheet often moves toward the lamp assembly through the gap between the guide members and the back cover. Such displacement degrades the displaying performance of the LCD unit.